1. Field of the Invention
The present invention relates to magnetic circuits and, more particularly, to apparatus and method for converting a static magnetic field to a time varying magnetic field.
2. Description of the Prior Art
In the science of electrical engineering the fundamental expressions of electromagnetism are defined by Ampere's Law. These relationships set out the magnetic quantities in terms of force, magnetic flux density, magnetic field intensity, permeability and similar factors.
It is well known that the magnetic behavior of matter, itself, is defined at the microscopic level. Thus an atom will experience a torque when placed in a magnetic field, often referred to as the magnetic moment. This magnetic moment depends upon the positive charges of the nucleus spinning on its axis, the negative charge of the electrons spinning on their axes and the effect of the electrons moving in their orbits. In this model the orbital motion of the electrons and their spin far exceed the moment of the nuclear, spinning, protons and electromagnetism is dominantly an expression of electron momentum.
Frequently atoms combine into molecules in such manner that the orbital motion of the electrons cancel each other out and a magnetic moment close to zero is thus effected. Thus, most substances provide magnetic flux density which is close to that of free space.
An exception to this general class is the class of materials consisting principally of iron in which the relative permeability is many times greater than that of free space. This class of materials is referred to as the "ferromagnetic class" and it is on the basis of this class of materials that most electromechanical devices are based. This class of materials, like all metals, is crystalline in structure with the atoms arranged in a spaced lattice. Unlike all the other metals, however, iron exhibits domains of sub-crystalline segments of varying sizes and shapes in which all the atoms are aligned in the same direction. These domains act independently of each other and in unmagnetized iron the domains are aligned haphazardly. The net magnetic moment then is zero on a large scale of any specimen. Upon the application of external magnetic field all the domains align parallel to each other and a state is reached which is referred to as the "saturated state". Simply, no further increase in flux density will occur in response to any further increase in magnetizing force. It is this limit on flux density that is the subject of most material science investigations.
The inductance of a magnetic field, in turn, is expressed by relationships discovered by Faraday. The distinguishing and significant feature of inductance is that it makes itself felt in the presence of a changing current or a changing flux. Thus, in a flux changing device the voltage across the terminals of an inductor may be expressed as: EQU E=-Ndf/dt
In this relationship, N is the number of turns of the inductor coil. This generalized relationship is correct both for electromagnetic flux changes and for flux changes occurring as result of physical flux cutting motion.
Those skilled in the art will appreciate that the same effect may be obtained by changes in magnetic permeability. For example, a magnetic loop operated at saturation will produce electromagnetic results in the presence of a change in saturation. At saturation the potential energy of the magnetic loop is simply the function of sectional area. Thus, the losses normally occurring in the course of hysteresis are limited only to that portion of the magnetic loop that is actually taken in or out of the magnetic circuit.
These aspects are utilized to advantage in the apparatus and method disclosed herein.